Conversations are cooperatively achieved speech events. In introducing a new topic, there are specific procedures followed to close the old topic. Because these procedures take place over a series of utterances, both/all participants must cooperate to close a topic. Analysis of conversations among adults who know each other suggests that there are topic-ending utterances that mark disjunctive topic changes, in which participants make an obvious transition from one topic to another. These topic-ending indicators include: (1) summary assessments; (2) acknowledgement tokens; (3) repetition; (4) laughter; and (5) pauses. Summary assessments are likely to occur first, and pauses last, before the beginning of a new topic. These two indicators appeared to be the most powerful and most common, especially when they occur together. None of the other three appeared alone. All of the indicators occur elsewhere in conversation, but at topic endings they occur together in sequences of utterances alternating between participants. The use of several topic-ending indicators seems to show that both/all participants seek agreement on the closing of the first topic. This analysis supports the view of conversation as a collaborative event. (MSE)